As Ukrainian forces battle to retake the eastern city of Donetsk from pro-Russian rebels, the US is warning that any bid by Moscow to deliver aid over the border will be “viewed as an invasion”.

Humanitarian help for people displaced by the fighting has been proposed by Moscow.

But Washington’s ambassador to the UN says Russia voiced similar concerns for civilians in Georgia in 2008 – before going to war with the ex-Soviet republic.

“Given that Ukraine has allowed international humanitarian groups to deliver aid within its territory, there is no logical reason why Russia should seek to deliver it,” US Ambassador Samantha Power told a UN Security Council meeting on Ukraine on Friday.

“Therefore, any further unilateral intervention by Russia into Ukrainian territory, including one under the guise of providing humanitarian aid, would be completely unacceptable and deeply alarming. And it would be viewed as an invasion of Ukraine.”

Ukrainian guards said on Friday that mortars fired from Russian territory damaged a border post in the Luhansk region, injuring four soldiers.

Moscow denies arming the rebels or having any plan to send its own forces into eastern Ukraine.

But NATO claims Russia has 20,000 troops massed near the border and the US has described military exercises in southern Russia as “provocative”.

The Defence Ministry in Moscow said the exercises are now over, adding that the drills in the southern Astrakhan region 1,000 kilometres from the Ukraine border, had shown a “high level of cohesiveness” among troops.